Exposure apparatuses are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly that retains and positions a reticle, a lens assembly, a wafer stage assembly that retains and positions a semiconductor wafer, and a measurement system that monitors the position or movement of the reticle and the wafer.
One or both of the stage assemblies are often required to operate over a relatively large area. This can make the monitoring of the position and/or movement of the stage assembly difficult.